1. Field of the Invention
The present invention generally relates to a color filter and a manufacturing method thereof, in particular, to a color filter formed by inkjet printing and manufacturing method thereof.
2. Description of Related Art
The liquid crystal display (LCD) is becoming the main project of the display research and continuously towards the development of colorized display because the LCD has the advantages of low operation voltage, no radiation, light weight and small volume etc., which are not possessed by the cathode ray tube display (CRT).
The liquid crystal display can display full color picture by using a color filter. Recently, a manufacturing method of a color filter using inkjet printing is developed. At first, a black matrix is formed on a substrate to define a plurality of pixel areas. Then, Red/Green/Blue pigments are filled into the pixel areas using inkjet printing. And then, the pigments are solidified by thermal baking process.
The inkjet printing technique can coat the color pigment on the substrate directly to form the color filter, with the advantages that no mask or stencil is needed to form the color filter. So that, the manufacturing flow becomes easy and the problems resulted from using acid-base solutions will not be occurred. FIG. 1 is a cross-sectional view of a conventional color filter formed by using inkjet printing. Please refer to FIG. 1, the conventional color filter 100 includes a glass substrate 110 and a black matrix 120 formed on the glass substrate 110. The black matrix 120 defines a plurality of pixel areas P filled with color pigment 130. It is noted that the color pigment 130 is filled into the pixel areas P by using inkjet printing.
The ratio of solvent to solution of the color pigment 130 is about 70% to 80%, that is, 70% to 80% of the solution is solvent. In the process of solidifying the color pigment 130, a great deal of solvent is vaporized that makes the color pigment 130 constrict so that the pixel areas P cannot be fully filled with the color pigment 130. Moreover, in order to make the thickness of the solidified pigment layer be same as the thickness of the black matrix 120, the column of the color pigment 130 before being solidified must relatively larger than the capacity of the pixel area P, and the color pigment 130 is filled into the pixel areas P with high flow velocity. As a result, the color pigment 130 will spill out of the pixel areas P so that color mixing problem may occur. Accordingly, The column of the color pigment 130 may be limited to avoid the color pigment from spilling out of the pixel areas P and color mixing problem, however, this inevitably result in unfilled pixel areas P and insufficient color saturation instead.
Furthermore, a hydrophobic treatment is performed on the black matrix 120 to modify the surface tension of the color pigment 130 on the black matrix 120. As shown in FIG. 1, under the influence of the surface tension, an uneven surface of the color pigment 130, whose center is protuberant and circumambience is sunken, is appeared. The color filter 100 with uneven surface results in worse coverage of the film layers in the follow-up process, and the liquid crystal display having such a color filter 100 may suffer from mura phenomenon.
It is known from experiments that in the color filter 100, a specific relation exists between the film thickness Db of the black matrix 120 and the film thickness Dc of the color pigment 130. For example, the color pigment 130 is filled using inkjet printing at the film thickness Db of the black matrix 120 of 2 micron. After molding, if the maximal film thickness Dc of the color pigment 130 is equal to or slightly bigger than the film thickness Db of the black matrix 120, the difference of the color pigment 130 is about 0.5 micron to 0.8 micron. However, when the maximal film thickness Dc of the color pigment 130 is equal approximately from ⅓ to ½ of the film thickness Db of the black matrix 120, the difference of the film thickness Dc of the color pigment 130 is only about 0.1 micron. That is to say, when the film thickness Db of the black matrix 120 is three times or double larger than the film thickness De of the color pigment 130, the color pigment 130 has a uniform and even surface. However, the protruding black matrix 120 causes the problem of uneasy coverage of the follow-up film layer.
Accordingly, it is an important issue to avoid color pigment mixing as well as manufacture a color filter with uniform pigment thickness and even surface in manufacturing the color filter.